Materials with good stretchability and elasticity are needed to manufacture a variety of disposal and durable articles, such as incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. Stretchability and elasticity are performance attributes which can, for example, function to effectuate a closely conforming fit to the body of the wearer or to the frame of the item. While numerous materials are known to exhibit excellent stress-strain properties and elasticity at room temperatures, it is often desirable for elastic materials to provide a conforming or secure fit during repeated use, during extensions and retractions at elevated or depressed temperatures, or in automobile interiors during summer months. Elasticity at elevated temperatures is also important for maintaining tight tolerances throughout temperature cycles. In particular, elastic materials used for repeated wear clothing or garments must maintain their integrity and elastic performance after laundering.
Lycra®, a segmented polyurethane elastic material, is currently used in various durable fabrics. Similar to conventional uncrosslinked polyolefin-based elastic materials, articles made from Lycra® can lose their integrity, shape, and elastic properties when subjected to elevated temperatures. Thus, Lycra® is not suitable in many co-knitting applications with high temperature fibers, such as polyester fibers. Also, Lycra® tends to be cost prohibitive for many applications.
Propylene-based polymers having good elastic properties are known. See, for example, U.S. Pat. No. 6,525,157, the entire disclosure of which is hereby incorporated herein by reference. Use of such propylene-based polymers in fiber applications has been contemplated. For example, U.S. Pat. No. 6,342,565, the entire disclosure of which is hereby incorporated herein by reference, discloses a soft, set-resistant, annealed fiber comprising a blend of polyolefins. The blend has a flexural modulus less than or equal to 12,000 psi in/in and includes from 75 to 98 wt % of a first polymer component and from 2 to 25 wt % of a second polymer component. The first polymer component is a propylene-ethylene polymer having at least 80 wt % propylene and up to 20 wt % ethylene, a melting point by DSC in the range of from 25 to 70° C., and a heat of fusion less than 25 J/g. The second polymer component is a stereoregular isotactic polypropylene having a melting point by DSC of greater than 130° C., and a heat of fusion greater than 120 J/g. The fiber exhibits a resistance to set equal to or less than 80% from a 400% tensile deformation. The polyolefin blend is said to be substantially non-crosslinked.